Analogous to ShowT; allows construction of Delay[RenderTree, F] for
an F that refers to T[... F ...].
final case classRenderedTree(nodeType: slamdata.Predef.List[slamdata.Predef.String], label: slamdata.Predef.Option[slamdata.Predef.String], children: slamdata.Predef.List[RenderedTree]) extends Product with Serializable